The invention is based on a pump unit.
A pump unit, which is comprised of a piston pump and a drive motor that drives the piston pump, has already been disclosed by DE 44 30 909 A1 and U.S. Pat. No. 5,564,909. The pump pistons of the piston pump are disposed in a pump block to which the motor housing of the drive motor is flange mounted. A shaft, which is driven by the drive motor and protrudes from the motor housing into the pump block, is used to drive the pump pistons of the piston pump. The motor housing has a projection which protrudes into a recess provided in the pump block. This projection of the motor housing contains a bearing which is supported on the shaft.
In the pump unit disclosed by DE 44 30 909 A1 and U.S. Pat. No. 5,564,909, it is disadvantageous that the bearing forces which arise at the center bearing cannot be optimally absorbed by the motor housing. DE 195 36 794 A1 has disclosed an embodiment which attempts to solve this problem by virtue of the fact that the bearing is built directly into the pump block between the drive motor and the pump pistons. However, this produces considerable technical manufacturing difficulties because with this embodiment, it is not possible to carry out a separate assembly and a possible separate testing of the drive motor before mounting the motor onto the pump block.
It has turned out that the connection, which is not optimally play-free, between the drive motor and the pump block contributes to the generation of noise.
In DE 44 30 909 A1 and U.S. Pat. No. 5,564,909, a radial clearance fit is disposed between the end of the shaft protruding into the pump block and the inner bearing ring of the bearing, there so that it is possible to assemble the components. With this bearing there is also the problem that this clearance fit also contributes to the generation of noise.
Because tolerances and clearance fits cannot be entirely avoided despite extremely high manufacturing precision, unpleasant noise produced by them must be expected.
DE 44 30 909 A1 and U.S. Pat. No. 5,564,909 disclosed pump units in which, the shaft is supported by means of an additional bearing in the motor housing, on the end remote from the pump block. However, the cost of manufacturing this bearing and the considerable space requirement for this bearing have up to now been significant disadvantages.